UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 6)

MARCUS & MILLICHAP, INC.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

566324109

(CUSIP Number)

Alexander Yarmolinsky

Chief Financial Officer

Phoenix Investments Holdings LLC

777 S. California Avenue

Palo Alto, CA 94304

(650) 494-1400

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

November 16, 2017

(Date of Event Which Requires Filing of this Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. ☐

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See §240.13d-7 for other parties to whom copies are to be sent.

The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

(Continued on following pages)

SCHEDULE 13D

SCHEDULE 13D

Explanatory Note

This Amendment No. 6 to the statement on Schedule 13D (“Amendment No. 6”) relates to the common stock, par value $0.0001 per share, of Marcus & Millichap, Inc.

George M. Marcus, Ionian Investments Manager LLC, and Phoenix Investments Holdings LLC filed the initial statement on Schedule 13D on November 12, 2013 (the “Initial Statement”) and capitalized terms used in this Amendment No. 6, but not otherwise defined, have the meanings given to them in the Initial Statement. This Amendment No. 6 amends and supplements the disclosures under Item 4 and amends and restates the disclosures in the cover pages hereto and Items 5 and 7 of Amendment No. 5 to the Initial Statement filed on March 24, 2017 (“Amendment No. 5”).

Item 4. Purpose of Transaction.

Item 4 of Amendment No. 5 is hereby amended and supplemented by deleting the disclosure under paragraph (j) and adding the following in its place:

“Except as described in this Item 4 and potential pro rata distributions to Pheonix’s members, the Reporting Persons do not have, as of the date of this Amendment No. 6, any other plans or proposals that relate to or would result in any of the actions or events specified in clauses (a) through (i) of Item 4 of Schedule 13D. The Reporting Persons may change their plans or proposals in the future. In determining from time to time whether to sell or to distribute to Phoenix’s members the MMI Common Stock reported as beneficially owned in this Schedule 13D, as amended, (and in what amounts) or to retain such securities, the Reporting Persons will take into consideration such factors as they deem relevant, including the business and prospects of the Issuer, anticipated future developments concerning the Issuer, existing and anticipated market conditions from time to time, general economic conditions, regulatory matters, and other opportunities available to the Reporting Persons. The Reporting Persons reserve the right to acquire additional securities of the Issuer in the open market, in privately negotiated transactions (which may be with the Issuer or with third parties), or otherwise; to dispose of all or a portion of their holdings of securities of the Issuer; or to change their intention with respect to any or all of the matters referred to in this Item 4.”

Item 5. Interest in Securities of the Issuer.

Item 5 of Amendment No. 5 is hereby amended and restated by the following:

“(a) Based on the Issuer’s Form 10-Q filed on November 9, 2017, 38,140,801 shares of MMI Common Stock were outstanding as of November 2, 2017. As of November 28, 2017, the Reporting Persons beneficially own the following amounts of MMI Common Stock:

Mr. Marcus’ beneficial ownership consists of:

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The Reporting Persons have the sole power to dispose or direct the disposition of the following amounts of MMI Common Stock:

The Reporting Persons have the shared power to vote or direct the vote of the following amounts of MMI Common Stock:

As noted above, Mr. Marcus’ shared power to vote or direct the vote consist of (i) 393,846 shares held directly by the George and Judy Marcus Foundation II of which Mr. Marcus, as trustee, may direct the vote, and (ii) 18,612,767 shares held directly by Phoenix of which Mr. Marcus, as the sole member and manager of Ionian, may direct the vote. Ionian, as the sole non-member manager of Phoenix, shares with Phoenix the power to vote the 18,612,767 shares held directly by Phoenix.

The Reporting Persons have shared power to dispose or direct the disposition of the following amounts of MMI Common Stock:

As noted above, Mr. Marcus’ shared power to dispose or direct the disposition consists of (i) 393,846 shares held directly by the George and Judy Marcus Foundation II of which Mr. Marcus, as trustee, may direct the disposition, and (ii) 18,612,767 shares held directly by Phoenix of which Mr. Marcus, as the sole member and manager of Ionian, may direct the disposition. Ionian, as the sole non-member manager of Phoenix, shares with Phoenix the power to dispose the 18,612,767 shares held directly by Phoenix.

On November 10, 2017, Phoenix sold 16,819 shares of MMI Common Stock at an average price of $30.3448 per share pursuant to Rule 144 of the Securities Act.

On November 13, 2017, Phoenix sold 26,138 shares of MMI Common Stock at an average price of $29.9698 per share pursuant to Rule 144 of the Securities Act.

On November 14, 2017, Phoenix sold 132,606 shares of MMI Common Stock at an average price of $30.6959 per share pursuant to Rule 144 of the Securities Act.

On November 15, 2017, Phoenix sold 141,101 shares of MMI Common Stock at an average price of $30.3484 per share pursuant to Rule 144 of the Securities Act.

On November 16, 2017, Phoenix sold 100,000 shares of MMI Common Stock at an average price of $30.5446 per share pursuant to Rule 144 of the Securities Act.

On November 17, 2017, Phoenix sold 243,898 shares of MMI Common Stock at an average price of $30.4977 per share pursuant to Rule 144 of the Securities Act.

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On November 20, 2017, Phoenix sold 188,826 shares of MMI Common Stock at an average price of $30.5241 per share pursuant to Rule 144 of the Securities Act.

On November 21, 2017, Phoenix sold 136,363 shares of MMI Common Stock at an average price of $31.0009 per share pursuant to Rule 144 of the Securities Act.

On November 22, 2017, Phoenix sold 50,839 shares of MMI Common Stock at an average price of $30.7549 per share pursuant to Rule 144 of the Securities Act.

Item 7. Material to be filed as Exhibits.

Item 7 of Amendment No. 5 is hereby amended and restated by the following:

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SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: November 29, 2017

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EXHIBIT A

JOINT FILING AGREEMENT

Each of the undersigned hereby agrees that the Schedule 13D, to which this Agreement is attached as Exhibit A, and all amendments thereto may be filed on behalf of each such person.

Dated: November 29, 2017

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